(1) Field of the Invention
The present invention relates to a harvester for a forestry machine, comprising grapple means for grasping a tree stem, a cutting tool for cutting off the tree stem, a limbing or trimming device for trimming the tree stem, advancement means for advancing the tree stem in the axial direction past the trimming device and the cutting tool, a measurement device for measuring the length of the tree stem and a measurement device for measuring how the transverse dimension of the tree stem varies along its length, this measurement device including movable measurement means for contact-free detection of the outer contour of the tree stem, from which its diameter is calculable.
The present invention further relates to a method of measuring the transverse dimension of a tree stem in connection with felling thereof, the tree stem being moved axially past a measurement device in a harvester, comprising the steps that a pair of measurement means are moved towards the tree stem, that pairs of read-off values are registered on detection of the outer contour of the tree stem, and that the transverse dimension of the tree stem is calculated from each pair of read-off values.
(2) Prior Art
In the felling of forest in modern, rational forestry, it is extremely important to monitor dimensions and volumes of those trees that a felled, in order that correct deliveries can be made to sawmills, pulp industries and other recipients of the felled trees. In such instance, the outer contour of the tree stems is sensed in at least two points lying in register with each other, and the distance between the points gives an approximation of the diameter of the tree stem. Granted, it may happen that a tree stem is oval and, in such instance, a measurement is taken of its minor axis which is considerably shorter than its major axis, but in the measurement of a large number of tree stems, the random variation of the measured transverse dimensions will on average give an acceptable sum total of the calculated volumes.
Today, the measurement of the extent of the tree stem is often put into effect using the knives disposed on the forestry machine for the trimming operation which wholly or partly surround the felled tree stem. The measurement using the knives is imprecise, since the knives cannot follow any possible inward depressions in the tree stem, but adjust themselves in response to the most projecting area of the stem. There are always larger or smaller air pockets inside the knives which in themselves are rigid.
Another method that has been tried is to dispose on the machine a frame with fixed photocells in a large number of positions. Depending on whether the light to the photocells is broken or not, the outer contour of the tree stem can be detected. One problem inherent in such frames is that they are sensitive to disturbance, since they contain many photocells which must all function in order to obtain a correct result. Another difficulty inherent in photocell frames is that they are sensitive to dirt, bark, branches, gravel and the like. Finally, such constructions are expensive to manufacture and maintain.
Those apparatuses with movable measurement means which are available, for example for measuring complex tubular structures and the like are thus far too fragile and expensive to be practically usable in a forestry machine.
There is thus a need in the art to realise a harvester with a measurement device which is sufficiently robust to function under the conditions prevailing at the felling site with the sought-for accuracy.